If you suspect something in an image update has broken your build, the first thing to try is the Previous image, as described here.
This is not meant as a permanent solution, but will allow us to determine whether or not the problem is indeed with the new image.

Ahh, figured it out! We were installing perl during the build process, but
it was grabbing a newer perl than the one supported by the base image.
Running 'pacman -Syu' forced it to upgrade the whole system, which got
everything synced up.